This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Previous work in our lab and data in the literature have consistently suggested that the Human apolipoprotein A-I (ApoA-I), is the principal protein component of high-density lipoprotein (HDL), which has a major function in transferring cholesterol from non-hepatic tissues back to the liver and thus plays a critical role in protection against atherosclerosis. The intrinsic flexibility of apoA-I allows its structure to adapt multiple conformations on different species of HDL that contain different amounts of phospholipids and cholesterol. Previous studies from our work and that of others has suggested the close proximity and thus the interaction between the N- and C-termini of ApoA-I in lipid- free conformation. The conformation and interaction of two peptide models, representing the N-terminal (residues 1-44) and C-terminal (residues 198-243) of apoA-I, have been investigated in lipid- free and lipid- bound forms by mass spectrometry and other methods. A manuscript describing our results is under revision. This requires a few additional experiments that are now being planned.